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Orthopaedics
Neurology

Cavovarus Foot

High EvidenceUpdated: 2025-12-26

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Red Flags

  • Unilateral Deformity -> Spinal Tumor (MRI Spine mandatory)
  • Rapid Progression -> Motor Neuron Disease?
  • Hand Wasting -> CMT
  • Stress Fractures -> Lateral column overload
Overview

Cavovarus Foot

1. Clinical Overview

Summary

A "Cavovarus" foot is characterized by a high arch (Cavus) and a heel that angulates inward (Varus). Unlike flatfoot, which is often flexible and asymptomatic, cavovarus deformity is rigid and rarely normal. It acts as a stiff "tripod", overloading the lateral border of the foot (5th metatarsal) and the ankle ligaments. Neuromuscular disease (classically Charcot-Marie-Tooth) is the cause in 66% of cases. The deformity is progressive: muscle imbalances (strong Peroneus Longus vs weak Tibialis Anterior) twist the foot until bones deform. Treatment aims to rebalance the muscles (tendon transfers) and realign the bones (osteotomies) before arthritis sets in. [1,2,3]

Key Facts

  • The Rule of 3s:
    • 33% have Charcot-Marie-Tooth (CMT).
    • 33% have another Neurologic cause (Spinal tumor, spinal dysraphism, CP, Stroke).
    • 33% are Idiopathic (Subtle Cavus).
    • Therefore, nearly 70% of high arched feet are neurologic. Work them up!
  • The Primary Driver: In most cases, the deformity starts in the forefoot. A strong Peroneus Longus pulls the 1st Ray down (plantarflexed). To put the foot flat on the ground, the heel acts as a tripod leg and must tilt into Varus. This is "Forefoot Driven Hindfoot Varus".
  • The Coleman Block Test: The crucial exam maneuver. By placing a block under the heel and lateral foot (letting the 1st ray hang free), we eliminate the forefoot deforming force. If the heel straightens out (corrects to valgus), the problem is the forefoot (Flexible). If it stays varus, the problem is the hindfoot (Fixed).

Clinical Pearls

"Peek-a-Boo Heel": When examining the patient from the front, you can see the medial side of their heel peeking out from behind the tibia. This is the sign of severe varus.

"Look at the Spine": If a patient presents with a Unilateral high arch, you MUST get an MRI of the entire spine. This is a spinal cord tumor (Syrinx or Ependymoma) until proven otherwise. CMT is bilateral.

"The Tripod": Imagine a three-legged stool (Heel, 1st Met, 5th Met). If the 1st Met leg is too long (plantarflexed), the stool tips over. Shortening that leg (Osteotomy) rights the stool.

2. Epidemiology

Demographics

  • Age: Adolescence (CMT presents).
  • Genetics: CMT is hereditary (Autosomal Dominant usually).
  • Etiology:
    • CMT (HMSN): Most common.
    • Spina Bifida.
    • Polio.
    • Cerebral Palsy.
    • Trauma (Compartment Syndrome sequelae).
3. Pathophysiology

The Imbalance (CMT Pattern)

  • Weak:
    • Tibialis Anterior (Dorsiflexion).
    • Peroneus Brevis (Eversion).
    • Intrinsics (Toe extension).
  • Strong:
    • Peroneus Longus (Plantarflexion of 1st Ray).
    • Tibialis Posterior (Inversion).
  • Result:
    1. PL pulls 1st ray down -> Cavus.
    2. TP pulls heel in -> Varus.
    3. EDL recruits to help weak TA -> Claw Toes.
4. Clinical Presentation

Symptoms

Signs

Instability
Recurrent ankle sprains (lateral ligaments fail under varus strain).
Pain
Lateral border of foot (5th metatarsal overload).
Clumsiness
"I trip over my toes" (Drop foot).
5. Investigations

Imaging

  • X-Ray (Weight Bearing):
    • Lateral: Meary's Angle (Increased). Hibbs Angle. Calcaneal Pitch (>30 deg).
    • AP: Talocalcaneal angle (Parallel = Varus).
  • MRI: Spine (if unilateral).
  • NCS/EMG:
    • Confirms neuropathy type (Demyelinating vs Axonal).
6. Management Algorithm
                 HIGH ARCH FOOT
                       ↓
             COLEMAN BLOCK TEST?
            ┌──────────┴──────────┐
        CORRECTS               RIGID
    (Forefoot Driven)     (Hindfoot Fixed)
           ↓                      ↓
     SOFT TISSUE +          OSTEOTOMY +
    1st MET OSTEOTOMY     CALCANEAL OSTEOTOMY
           ↓                      ↓
        FAILED?                FAILED?
           ↓                      ↓
      TRIPLE FUSION          TRIPLE FUSION
7. Management: Conservative

Protocol

  • Orthotics:
    • Lateral Wedge: To push the heel out of varus (only if flexible).
    • Recess: Under 1st metatarsal head.
  • Bracing: AFO (Ankle Foot Orthosis) for drop foot.
8. Management: Surgical

Strategy: "A la Carte"

Reconstruction involves multiple steps customized to the deformity.

1. Soft Tissue Releases

  • Plantar Fascia Release: Stops the "windlass" effect holding the arch high.
  • Jones Procedure: Transfer EHL to Metatarsal neck to lift the foot (treats claw toe and drop foot).
  • Peroneus Longus to Brevis: Strengthens eversion.

2. Osteotomies (Bone Cuts)

  • 1st Metatarsal Dorsiflexion Osteotomy:
    • Reverses the plantarflexed 1st ray. Corrects the "Tripod".
  • Dwyer (Lateralizing Calcaneal) Osteotomy:
    • Shifts the heel bone laterally to correct varus.
    • Essential if Coleman block test shows rigid hindfoot.

3. Triple Arthrodesis

  • Indication: Rigidity + Arthritis. End stage.
  • Procedure: Fuse ST, TN, CC joints in a corrected plantigrade position.
9. Complications

Non-Union

  • Osteotomies heal generally well, but non-union occurs.

Recurrence

  • If the underlying neurologic disease progresses (e.g., severe CMT), the deformity can return even after reconstruction.

Over-correction

  • Turning a high arch into a flatfoot (Valgus).
10. Evidence & Guidelines

Joint Sparing vs Fusion

  • Wukich et al: Joint-sparing reconstruction (Osteotomies + Tendon Transfers) provides better long-term function and shock absorption than Triple Arthrodesis. Fusion should be reserved for salvage.

The 1st Ray

  • Paulos et al: Emphasized that the First Ray is the key to the deformity. Addressing the heel without lifting the 1st metatarsal will fail.
11. Patient Explanation

The Shape

Your foot is shaped like a tripod with one leg too long (the big toe bone). Because that leg is long, your heel has to tip over to touch the ground.

The Fix

We don't just fuse it. We remodel it.

  1. Cut the fascia: Relax the bowstring.
  2. Cut the toe bone: Shorten the long leg of the tripod.
  3. Slide the heel: Push it back under your leg.
  4. Move tendons: Rebalance the steering.
12. References
  1. Mann RA, Missirian J. Pathophysiology of Charcot-Marie-Tooth disease. Clin Orthop Relat Res. 1988.
  2. Coleman SS, Chestnut WJ. A simple test for hindfoot flexibility in the cavovarus foot. Clin Orthop Relat Res. 1977.
  3. Wukich DK, Bowen CJ. A long-term study of triple arthrodesis for correction of cavovarus deformity. Foot Ankle Int. 2000.
13. Examination Focus (Viva Vault)

Q1: Describe the mechanics of the Coleman Block Test. A: The patient stands with the heel and lateral border of the foot on a 1-inch wooden block, while the 1st Metatarsal hangs free over the medial edge. This neutralizes the plantarflexed 1st ray.

  • If the hindfoot corrects to valgus -> The varus is flexible and driven by the forefoot.
  • If the hindfoot remains in varus -> The varus is fixed (requires calcaneal osteotomy).

Q2: Which muscles are weak in Charcot-Marie-Tooth? A: Anterior (Tibialis Anterior) and Lateral (Peroneus Brevis) compartments.

  • Note: Peroneus Longus remains strong, usually.

Q3: What is the "Jones Procedure" for cavus foot? A: Transfer of the Extensor Hallucis Longus (EHL) tendon to the neck of the 1st Metatarsal + Fusion of the IP joint of the big toe.

  • Purpose: 1) Removes the deforming force causing claw toe. 2) Uses the EHL to dorsiflex the ankle (treating drop foot).

Q4: Why is the Peroneus Longus a deforming force? A: It inserts on the base of the 1st metatarsal. Its primary action is plantarflexion of the 1st ray. When unopposed by the weak Tibialis Anterior, it pulls the 1st ray down, creating the cavus arch and driving the forefoot into valgus/pronation relative to the hindfoot.

(End of Topic)

Last updated: 2025-12-26

At a Glance

EvidenceHigh
Last Updated2025-12-26

Red Flags

  • Unilateral Deformity -> Spinal Tumor (MRI Spine mandatory)
  • Rapid Progression -> Motor Neuron Disease?
  • Hand Wasting -> CMT
  • Stress Fractures -> Lateral column overload

Clinical Pearls

  • **"Peek-a-Boo Heel"**: When examining the patient from the front, you can see the medial side of their heel peeking out from behind the tibia. This is the sign of severe varus.
  • **"The Tripod"**: Imagine a three-legged stool (Heel, 1st Met, 5th Met). If the 1st Met leg is too long (plantarflexed), the stool tips over. Shortening that leg (Osteotomy) rights the stool.
  • The varus is flexible and driven by the forefoot.
  • The varus is fixed (requires calcaneal osteotomy).

Guidelines

  • NICE Guidelines
  • BTS Guidelines
  • RCUK Guidelines